Fortescue Metals Group's removal of asbestos from about 3400 Chinese rail cars is being done without sufficient safety precautions, according to the union that represents rail maintenance workers.
In 2017 FMG discovered white asbestos in friction wear plates in the suspension systems of 3384 rail cars and reported it to the safety regulator.
WorkSafe issued an improvement notice to FMG in September 2017 giving the Andrew Forrest-chaired iron ore miner two years to remove the asbestos.
WorkSafe had notified rail operators in 2013 that asbestos had been found in some friction plates.
Australian Manufacturing Worker's Union assistant secretary Glenn McLaren yesterday visited FMG's Thomas Railyard near Port Hedland where the asbestos removal work is being done.
Mr McLaren said the work had started recently and about four cars per day were being completed.
"They're only cracking on a year after the improvement notice was issued," he said.
FMG chief executive Elizabeth Gaines said the iron ore miner had been testing potential replacement parts since he discovered the problem.
"Since October (2018), 958 of the 3384 cars have impacted their parts safely changed," she said.
Ms Gaines said FMG was on track to complete the work by the regulators' September 2019 deadline.
Mr McLaren said the asbestos removal workers had inadequate decontamination facilities.
He said they were hosing themselves down at the end of a shift with a hand pumped water spray as used by gardeners.
The union-leader said he was concerned that other workers near the asbestos removal work could be exposed to deadly fibers.
He said the bunded zone to separate the work areas "is two witches hats with a bit of tape over it."
"That's not going to contain asbestos particulate matter," he said.
Ms Gaines said the work complied with the code of practice for the removal of non-friable asbestos.
Friable asbestos, that can easily crumble into dust, is the more dangerous form of the fibrous material.
Mr McLaren said his members had maintained some of the affected rail cars for a decade.
"There has been no worker surveillance or health monitoring," he said.
Ms Gaines said independent monitoring from the outset had identified an extremely low risk of exposure for employees and periodic monitoring, which would continue, had continued to strengthen this.